Aural telephone system



@m 3Q, 1928, 1,689,692 H. SELL AURAL TELEPHONE SYSTEM Filed April 22, 1925 MICROPHONE AMPLIFIER ZICROPHZNIC QSPLIFIEES Patented Oct. 30, 1928.

UNITED STA TES PATENT o icE. I

'HELM'UT SELL, OF .BERLIN-SIEMENSSTAIDT, GERMANY, ASSIGNOR SIEMENS b HALSKE, AKTIENGESELLSCHAF'I, 0F SIEMENSSTADT, NEAR BERLIN, AND ELSE- WHERE, GERMANY.

- AURAL TELEPHONE SYSTEM.

Application filed April :22, 1925, Serial m. 24,986, and in Germany August 20, 1924.

' The present invention relates to improvements, in aural telephone systems for the deaf and for persons hard of hearing and the objectof the invention is to producean outfit of light weight, great sound-intensity, low current consumption and of such form and dimensions that the greater fpart of it may be hidden in the garments o the user.

The usual'hearing devices for the deaf and for persons hard of hearing comprise one or more microphones which-are fed from a dry battery and in the circuit of which an ear phone is placed. All such devices have the advantage that the fluctuations of C111.

rent which are created in the microphones when the sound waves are impressed upon the microphone diaphragms only form a very small part ofithe constant working current which passes through the microphones. In other wordsthe deflections caused by the sounds are minimal and'insufficient for the purpose intended the greater part of the current. being lost. Partly improved results may be obtained by using a relatively coarse contact material, for instance granulated carbon or carbon balls.

By this measure the sound intensity is increased but the clearness of articulation be- I cillations, provided that it gives a clear artic- N comes impaired; In order to intensify the sound it is necessary toarrange a great number'of contacts so that a good sound is secured as an average value of the several contacts. Vitho'ut this measure it is impossible to obtain a satisfactory result.

These disadvantages are removed by the present invention. In accordance with the same a microphone of any desired kind may be used for the reception of the sound os ulation. This is of more importance than its amplifying qualities. The currentfluctuations created in this microphone are used tocontrol electromagnetically a second microphone in the circuit of which the ear phone is located. It is advantageous also for the second microphone which is of extremely small dimensions, to use a non-sensitive but good-working contact arrangement and a'sufliciently damped diaphragm. The

c urre nt fluctuations or amplitudes of the seca much higher degree than in proportion to the lower consumption of current. It-is also possible at the same or a somewhat in: creased current consumption to increase the sound intensity immensely. It is for instance easy to reach a physical sound intensity which is a thousand times greater than the original physical sound intensity.

When using two amplifier microphones the first. of which is controlled by the pickup microphone and the second by the gg'st amplifier microphone a type is prefera l used for the first amplifier microphone whic i is very sensitive to the lowest intensities of current, but for the -second amplifier micr0- phone a type is chosen which gives a large amount of amplification. v P

Finally it is possible to decrease'the dimensions of the apparatus elements at the same consumption of current. A receiving disclosed for instance in the U. S. Patent No.

1,406,510 to Weber. Notwithstanding the small dimension of these foregoing elements, also the amplifier microphone may beof extremely small dimensions so that all parts of the apparatus except the ear phone may be hidden in the garments.

The invention is shown by way of examples in the accompanying drawings.

Fig. 1 shows a general diagram of -con-, nections.

Fig. 2 is a diagram of 'connections-ofan apparatus in which two amplifying microphones are used. 4

- The Figs. 3, 4 and 5 show some preferred "embodiments: of allthe apparatus.

. amplificatiom Fig. 6 is a vertical section through an amplifier-microphone of .the kind which is preferably used in thisapparatus, and

Figs. 7 and 8 show'a front anda ,rear view of the inner parts of the amplifier according to Fig. 6;

According to Fig. 1, 1 is a battery (usually of 3 to 4 volts) and 2 is a cut-out switch. 3 is the pick-up microphone which picks up and is actuated by the sound waves and 4 is the exciting winding of the controlled amplifier microphone 5, 6 denotes an adjustable series resistance and 7 the ear telephone.

In the example shown in Fig. 2 the'pick-up microphone 3 controls two am lifier microphones 5 and 8. The current rom the battery 1 passes over the pick up microphone 3 through the control windin 4 of the amplifier microphone 5, whereas t e current which the last named microphone receives from the battery 1 passes throu h the control windings 9 of the second ampli er microphone 8, over which the battery current of the telephone 7 adjustable by the resistance 6 is conducted. In other words the system represents a plurality of microphonic amplifyin devices in cascade connection. 'An ampli cation will therefore take place in two successive stages in the microphones 5 and 8.

The amplifier microphone 5 as well as th pick up microphone 3 are of such a type that they are as sensitive as possible and that their contact resistances change in response to the, smallest variations of sound waves respectivel of the current. On the other hand the amp ifier microphone 8 is constructed in such a manner that it will give a large amount of The arrangement of the elements of the outfit may be varied in many ways in accordance with the special use for which the apparatus is designed, as shown in the Figs. 4,

According to Fig. 3 two pick up microphones 3 and 3 are connected together by a frame 20. Each of them as well as the amplifier microphone 5 have an extremely small diameter, amounting only to about 30-min.

v The frame 20 can be fastened to a button in a dry battery 1 of such dimensions that it may be easily putinto a pocket of'the garments, these microphones being also connected to the amplifier microphone 5 arranged at the top of the battery and by strand 23to the eargphone 7. The earphone is of such aforman of such-dimensions that it maybe placed into the auditory passage'of. the ear. The

amplifier microphone 5 isprovided with In the frame 20 the cut-out switch for the battery 1 is arranged of which only the moving leyer 13 is. seen in the drawings. The adjustable resistance 6 is arranged in the strand 23 and a small pin 14 is provided for to make the adjustments.

According to the embodiment of the invention shown in Fig. 4 the pick-up microphone 3 is arranged ,on the top of the battery 1 and, when the latter put into a pocket of the waist-coat, the microphone will project from the pocket. The same will nevertheless hardly be observed on account of its small dimensions. Generally however the sound effect of the new device is so great that it almost always will be possible to hide also the pickup microphone in the garments, as the sound effect even through the garments will be suiiicicnt. i

In Fig. 5 the pick-up microphone 3 is connected with the amplifier microphone 5 by a frame 20 placed directly upon the socket 16 of the battery 1. In this modification only one line for the ear telephone 7 i'sanecessary and the rest of the apparatus may be laced in a pocket or in a ladys hand-bag.

he cut-out switch and the adjustable resistance, the adjusting buttonsor' levers 13, 14 of which alone are visible in that figure, are arranged at a suitable place inside of the frame 21.

Other combinations of the .apparatus elements are of course possible.

Figs. 6-8 show an embodiment of an amplifier microphone of a kind which on account of the small dimensions of its different elements and its other good properties is very well suited for use in the above described devices.

This apparatus consists of a casing 17 of hard rubber and a metallic cover 18 connected tov it by a thread 19 in which a magnet system and a. microphone controlled by that system are located. This magnet system may have asoft iron 'core or a permanent magnet core. The system shown is of the latter type.

It consists of a ring of steel 24 magnetized in diametral direction as indicated by the letters N and S in Fig. 8. To the south-pole S is rigidly connected a sector-shaped piece 25 of iron at the end ofwhich an iron pin 26 is arranged coaxially with the ring 24. To the lower part S of the ring magnet 24 a disc 28 of soft iron is fixed by a piece 27 of-non-magnetic material which disc is fixed to the upper disc 28 is provided with a projecting part 30 and with a radial slot 31 which preventsthe occurrence of short-circuit currents. In'the .plane of the projecting part 36 this part forms a north-pole and the end of thepin 26 a' south pole. On the pin 26 is. arranged the wlnding 48 controlling the microphone. The

.part N of the ring by an iron piece 29. The

magnet system is insertedinto the casing 17 and a sleeve 32, adapted to lead the communication strands 33 out of the casing, is guided in a slot 34 of the casing 17.

On the rim' of the disc 28 a distance ring 35 of non-magnetic metal is laid and upon this ring the microphone is arranged' The microphone comprises a diaphragm 35 which is of a high grade elastical material preferably phosphorebronze and of a thickness amounting only to a few hundred parts of a millimeter or less. The edge of this foil is soldered to a supporting ring 36 the ed e of which rests on the distance ring 35. .o

the central art of this foil a disc shaped iron armature 3 is soldered, which has a thickness of only some ,tenth part of a millimetre and a diameter of about 10 millimetres So that it just will cover the air gap between the poles 26 and 30 of the magnet system. The-foil or diaphragm 35' is kept permanently tensioned or stretched by means of a body 38 forming the microphone cell supplied with a ringshaped edge 39 pressed against the foil 35' by means of a ring 40 clamping together the sup.-

4 port ring 36 and the ed of the microphone cell 38. In the microp one cell a filling 41 preferably of granulated carbon is used as resistance material and theperipheral parts of the diaphragm are preferably damped by means of a felt ring 42, so that only thecentral part of the' diaphragm, which 'ves the strongest oscillations, comes into actlon.

In the bottom of the microphone cell 38 an opening is for ed into which a cylindrical projection 43 of a metal plate 44 projects in such manner that with its front side it presses against the carbon filling 41. This plate and also the entire microphone cell are held in place by the cover 18 of the casing 17.

v The electrical connection of the projection 43 is formed by a metal cap 45 put over the cover 18 at the edgeof which a bifurcated tongue 46 is arranged. This tongue is pushed over a screw 47 on the casing17. The strands of the cable 33 are connected to the plug pins 15, the screw 47 and diaphragm 35' respectively.

If according to Fig. 2 two amplifier microphones are made use of the ring of felt 42 in the first microphone is broad so that the cell has a diameter of only a few millimetres,

and the carbon filling 41 is very finely granulated. The second microphone 9, 8 contains a narrower felt ring so that the cell is proportionally large and the contact pressure is caused by the weight of the carbon filling.

WhatI claim as my invention and desire to secure by LettersPatent is:--

1. In an aural telephone systemofthe character described a-sound pick-up microphone,

at least one microphonic amplifier device electrically connected in cascade with said pick-up microphone, an ear phone, suitable conductors for connec ting said ear phone being electrically connected in cascade electrically connected in cascade with said pick-up microphone, an earphone, suitable conductors for connectmg said ear phone with said microphones and a-battery connected in parallel with said 1 mircrophones and with said ear phone, an adjustable resistance in circuit with said ear phone and a common cut-out switch between said battery and said microphones and ear phone.

3. In an aural telephone system of. the character described a sound pick-up microphone,

at least one microphonic amplifier device electrically connectedin cascade with said pickup microphone, an ear phone, suitable conductors for connecting said ear phone with said microphones, all of said microphones being mounted on a common base, a battery and a plug and socket connection between said base and said battery to make a rigid but separable unit of said two elements, said plug connecting the battery in parallel to said microphones and said ear phone, an adjustable resistance in circuit with said ear phone and a common cut-out switch between sailid battery and'said microphones and ear one.

4. In an aural telephone system of the character described a sound pick-up microphone, a microphonic amplifier device of small amplifying power electrically connected in cascade with said pick-up microphone, a microphonic amplifier device of large amplifying power electrically connected in cascade with said first amplifier device, an ear phone electrically connected with said second amplifier device and a battery connected in parallel with said pick-up microphone, said amplifiers and said ear phone.

.5. In an aural telephone system of the character described a sound pick-up microphone, amicrophonic. amplifier device of small amplifying power electrically connected'in cascade with said pick-up microphone, a microphonic amplifier 'device of large amplifying and said ear phone, an adjustable resistance in circuit with said ear phone a -d a common cutout switch between said battery and all of the aforesaid devices connected to'it.

6. In an aural telephone system of the character described a sound pick-up microphone, a microphonic-amplifier device having arela tively small microphone cell containing finem 1y granulatedcarbon, said amplifier device with said pick-up microphone, a second micro-v phonic amplifier device having a relatively large microphone cell contalnlng coarsely granulated carbon whose contact pressure is effected through its Weight, said second device being electrically connected in cascade with said first amplifier device to efiect first small amplification but great sensitiveand abattery connected in parallel with said pick-up microphone, said amplifier devices and said ear phones.

In testimony whereof I afiix my signature.

HELMUT SELL. 

